- Read Me First
- Preparing for Broadband Access Aggregation
- Providing Protocol Support for Broadband Access Aggregation of PPPoE Sessions
- PPP for IPv6
- DHCP for IPv6 Broadband
- Providing Protocol Support for Broadband Access Aggregation of PPP over ATM Sessions
- Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs
- PPPoE Circuit-Id Tag Processing
- Configuring PPP over Ethernet Session Limit Support
- PPPoE Session Limit Local Override
- PPPoE QinQ Support
- PPP-Max-Payload and IWF PPPoE Tag Support
- PPPoE Session Limiting on Inner QinQ VLAN
- PPPoE Agent Remote-ID and DSL Line Characteristics Enhancement
- Enabling PPPoE Relay Discovery and Service Selection Functionality
- Configuring Cisco Subscriber Service Switch Policies
- AAA Improvements for Broadband IPv6
- Per Session Queueing and Shaping for PPPoEoVLAN Using RADIUS
- 802.1P CoS Bit Set for PPP and PPPoE Control Frames
- PPP over Ethernet Client
- PPPoE Smart Server Selection
- Monitoring PPPoE Sessions with SNMP
- PPPoE on ATM
- PPPoE on Ethernet
- PPPoE over VLAN Enhancements Configuration Limit Removal and ATM Support
- ADSL Support in IPv6
- Broadband IPv6 Counter Support at LNS
- PPP IP Unique Address and Prefix Detection
- PPP IPv4 Address Conservation in Dual Stack Environments
- TR-069 Agent
- Broadband High Availability Stateful Switchover
- Broadband High Availability In-Service Software Upgrade
- Controlling Subscriber Bandwidth
- PPPoE Service Selection
- Disabling AC-name and AC-cookie Tags from PPPoE PADS
- Finding Feature Information
- Information About PPP-Max-Payload and IWF PPPoE Tag Support
- How to Configure PPP-Max-Payload and IWF PPPoE Tag Support
- Configuration Examples for PPP-Max Payload and IWF PPPoE Tag Support
- Additional References
- Feature Information for PPP-Max-Payload and IWF PPPoE Tag Support
PPP-Max-Payload and IWF PPPoE Tag Support
The PPP-Max-Payload and IWF PPPoE Tag Support feature enables the PPP over Ethernet (PPPoE) component to process the PPP-Max-Payload and Interworking Functionality (IWF) PPPoE tags in the PPPoE discovery frame:
The tag ppp-max-payload command allows PPPoE peers to negotiate PPP maximum receive units (MRUs) greater than 1492 octets if the underlying network supports a maximum transmission unit (MTU) size greater than 1500 octets.
The IWF PPPoE tag allows the Broadband Remote Access Server (BRAS) to distinguish the IWF PPPoE from the regular PPPoE sessions to overcome the per-MAC session limit put on the BRAS as a protection from denial of service (DOS) attacks sourced from the same MAC address.
- Finding Feature Information
- Information About PPP-Max-Payload and IWF PPPoE Tag Support
- How to Configure PPP-Max-Payload and IWF PPPoE Tag Support
- Configuration Examples for PPP-Max Payload and IWF PPPoE Tag Support
- Additional References
- Feature Information for PPP-Max-Payload and IWF PPPoE Tag Support
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Information About PPP-Max-Payload and IWF PPPoE Tag Support
Accommodating an MTU MRU Greater than 1492 in PPPoE
Per the RFC, "Accommodating an MTU/MRU Greater than 1492 in PPPoE," PPPoE peers can negotiate only MRUs with a maximum of 1492 octets so that the PPPoE header and PPP protocol ID can be inserted in the PPPoE session data packet. The maximum for an Ethernet payload is 1500 octets.
RFC 2516 defines a new tag to allow PPPoE peers to negotiate PPP MRU greater than 1492 if the underlying networks can support an Ethernet payload of greater than 1500 bytes. To enable processing of this new tag, a command has been defined in the Cisco IOS command-line interface as tag ppp-max-payload.The PPP-Max-Payload and IWF PPPoE Tag Support feature enhances the PPPoE component so the tag ppp-max-payloadcommand can process the new tag to influence the Link Control Protocol (LCP) MRU negotiations for the PPP session based on the MRU value specified in the tag from the PPPoE client.
Interworking Functionality
The DSL Forum defined IWF to define the process for conversion of PPP over ATM (PPPoA) sessions to PPPoE sessions at the digital subscriber line access multiplexer (DSLAM) to the BRAS. This functionality was defined to help the migration of DSLAM networks from ATM to Ethernet media. So, essentially, the PPPoA session comes in to the DSLAM over ATM and is converted to a PPPoE session at the DSLAM, which is then connected to the BRAS as a PPPoE session. Each PPPoA session is mapped to a corresponding PPPoE session.
Typically, the BRAS is configured to limit PPPoE sessions originating from the same MAC address to protect itself from a DOS attack. This presents a problem for IWF PPPoE sessions because all PPPoE sessions originate from the same MAC address DSLAM. To overcome this issue, the IWF PPPoE tag is inserted at the DSLAM and read by the BRAS to distinguish the IWF PPPoE session from the regular PPPoE session during the PPPoE discovery frames.
For more information about this subject, refer to the DSL Forum Technical Report 101, "Migration to Ethernet-Based DSL Aggregation."
How to Configure PPP-Max-Payload and IWF PPPoE Tag Support
- Enabling PPP-Max-Payload and IWF PPPoE Tag Support
- Disabling PPP-Max-Payload and IWF PPPoE Tag Support
Enabling PPP-Max-Payload and IWF PPPoE Tag Support
To enable the PPP-Max-Payload and IWF PPPoE Tag Support feature, perform this task.
1.
enable
2.
configure
terminal
3.
bba-group
pppoe
{group-name | global}
4.
virtual-template
template-number
5.
tag
ppp-max-payload
[minimum value maximum value] [deny]
6.
sessions
per-mac
iwf
limit
per-mac-limit
7.
interface
{fastethernet | gigabitethernet | tengigabitethernet} slot /subslot/ port[subinterface]
8.
pppoe
enable
[group
group-name]
9.
virtual-template
template-number
10.
ppp
lcp
echo
mru
verify
[minimum value]
11.
end
12.
show
pppoe
session
[all| packets]
DETAILED STEPS
Disabling PPP-Max-Payload and IWF PPPoE Tag Support
The tag ppp-max-payload command adjusts PPP MTU of the PPPoE session above the default maximum limit of 1492 bytes. But MTU values greater than 1492 can only be supported (with PPPoE) if the underlying Ethernet network supports these larger frames. Not all Ethernet networks support higher values. If your network does not support values higher than the default maximum, you should disable the PPP-Max-Payload and IWF PPPoE Tag Support feature by performing this task.
1.
enable
2.
configure
terminal
3.
bba-group
pppoe
{group-name | global}
4.
tag
ppp-max-payload
deny
DETAILED STEPS
Configuration Examples for PPP-Max Payload and IWF PPPoE Tag Support
This section provides a sample configuration showing the PPP-Max-Payload and IWF PPPoE Tag Support feature enabled and a configuration in which the effects of this feature are disabled:
- PPP-Max-Payload and IWF PPPoE Tag Support Enabled Example
- PPP-Max-Payload and IWF PPPoE Tag Support Disabled Example
PPP-Max-Payload and IWF PPPoE Tag Support Enabled Example
The following configuration example shows the PPP-Max-Payload and IWF PPPoE Tag Support enabled to accept PPP-Max-Payload tag values from 1492 to 1892, limits the number of sessions per MAC address to 2000 when the IWF is present, and verifies that the PPP session can accept 1500-byte packets in both directions:
bba-group pppoe global virtual-template 1 tag ppp-max-payload minimum 1492 maximum 1892 sessions per-mac limit 1 sessions per-mac iwf limit 2000 ppp lcp echo mru verify ! interface Virtual-Template 1 !
PPP-Max-Payload and IWF PPPoE Tag Support Disabled Example
The following configuration example disables the effect of the tag ppp-max-payload command:
bba-group pppoe global virtual-template 1 tag ppp-max-payload deny
Additional References
The following sections provide references related to the PPP-Max-Payload and IWF PPPoE Tag Support feature.
Related Documents
Related Topic |
Document Title |
---|---|
Additional information about commands used in this document |
Standards
Standard |
Title |
---|---|
DSL Forum Technical Report 101 |
MIBs
MIB |
MIBs Link |
---|---|
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature. |
To locate and download MIBs for selected platforms, Cisco IOS XE releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
RFCs |
Title |
---|---|
RFC 2516 |
|
Draft RFC document |
Technical Assistance
Description |
Link |
---|---|
The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password. |
Feature Information for PPP-Max-Payload and IWF PPPoE Tag Support
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Feature Name |
Releases |
Feature Information |
---|---|---|
PPP-Max Payload and IWF PPPoE Tag Support |
Cisco IOS XE Release 2.3 |
This feature was introduced on Cisco ASR 1000 Series Routers. This feature enables the PPP over Ethernet (PPPoE) component to process the PPP-Max-Payload and Interworking Functionality (IWF) PPPoE tags in the PPPoE discovery frame. The following commands were introduced or modified: ppp lcp echo mru verify, sessions per-mac iwf limit, show pppoe session, tag ppp-max-payload. |